Drive pinion for actuating a rapier rod in a weaving machine

ABSTRACT

This invention is related to a drive pinion ( 1 ) for actuating a rapier rod ( 2 ) of a weaving machine, whereby interaction of rapier rod ( 2 ) with drive pinion ( 1 ) is subject to less hindrance and damage due to occurring impact load at increased operational speeds and/or larger weaving widths, in that the tooth thickness (Td) of at least one tooth ( 3 ) of the drive pinion ( 1 ) varies in widthwise-direction (Tb) of the tooth ( 3 ), and whereby this tooth thickness (Td) is larger in the middle area ( 5 ) than in the fringe areas ( 7 ).

The invention relates to a drive pinion for actuating a rapier rod of a weaving machine, comprising a set of teeth, which are disposed in such a way that they engage the tooth profile of a cooperating rapier rod on the one hand, and to a rapier device for a weaving machine, comprising a rapier rod actuated by a drive pinion according to the invention on the other hand.

This patent application relates furthermore to a rapier-weaving machine equipped with one or more rapier devices according to the invention.

In a rapier-weaving machine, the rapiers, that carry the weft yarn through the shed from one side of the weaving machine to the other side of the weaving machine, are each of them at their end connected to a rapier rod. For performing the back-and forth motion, this rapier rod is guided in a guiding device. For actuating this back-and-forth motion, the rapier rod is provided with a tooth profile, which meshes with a drive pinion fitted at the vertical axis. The tooth profile is preferably achieved in providing rectangular apertures or cutouts in the rapier rod.

Given the tendency of manufacturing and using rapier-weaving machines with ever increasing operational speeds and machines with an increased weaving width, speed at which the rapier rod has to move through the shed also increases. Moreover, at one end of its motion, the rapier has to pick up or drop off the weft yarn and at the other end of its motion it has to pass on or take over the weft yarn. At these ends, the rapier always stops and next it takes up its full moving speed again in the other direction.

Considerable impact forces occur during this reverse of motion, and these forces strongly increase with accelerating operational speed of the weaving machine and with accelerating operational speed of the rapier rod. These impact forces also have an influence on the spot where the teeth of the rapier rod and the teeth of the cooperating gear pinion interact with each other.

In the present state of technique, this force is limited or absorbed in manufacturing the rapier rod, the drive pinion or both parts out of either materials having a reduced weight, or out of materials that are stronger or materials that combine these two features. In this way the German patent publication DE 3527202 discloses a rapier rod made out of synthetic material in order to limit stress by reducing inertia.

Stiffness of synthetic materials, however, is much lower, due to which interaction with pinion (mostly manufactured from steel or aluminum) will lead to it that the synthetic teeth of the rapier rod deform.

This deformation causes Hertzian stresses between pinion and rapier rod, which reach peaks in the fringe area of the tooth width at the outer side of the teeth of the pinion. This phenomenon has two drawbacks: on the one hand because the higher stress is locally considerably higher compared to when an even spread of the Hertzian stress would be achieved, due to which overload may occur locally; on the other hand this higher load occurs near the roundings of the rapier rod teeth, which is a drawback in its turn because of a higher risk of notch effect at this spot.

Because of the limitations in stiffness of the plastic rapier rod, the German patent publication DE 3638673 discloses an embodiment of the rapier rod, in which the plastic is reinforced by using fiber composite materials in the plastic such as for instance: glass fibers, carbon fibers or armid fibers. These rapier rods, however, are difficult to manufacture and expensive.

It is the aim of the invention to manufacture in a simple way and at acceptable cost price a drive pinion for actuating a rapier rod of a weaving machine, in which the interaction of the rapier rod with the drive pinion is subject to less hindrance and damage due to occurring impact load at increased operational speeds and/or larger weaving widths.

The aim of the invention has been achieved in providing a drive pinion for actuating a rapier rod of a weaving machine, comprising a set of teeth that are disposed to engage a tooth profile of a cooperating rapier rod, in which tooth thickness of at least one tooth of the drive pinion varies according to the widthwise-direction of the tooth and in which this tooth thickness is larger in the middle area than it is at the fringe area.

In this patent application “according to the widthwise-direction” should be understood as the direction transversely to the outline (centre line) of the pinion.

In adapting the shape of the teeth of the drive pinion and in this way shape a preferably crowned teeth profile, a reduced impact load between rapier rod and drive pinion is achieved.

In a more particular embodiment of the drive pinion according to the invention, tooth thickness progressively reduces from the middle area on. In slightly reducing the tooth thickness of a number of teeth in widthwise-direction of the pinion from the middle of the tooth width to the outside (fringe area) of the tooth width, stress would theoretically be concentrated in the middle of the teeth, which would also mean a harmful load. Now it has been shown that due to the deformation of the less stiff tooth apertures in the rapier rod, these deformed tooth apertures in the rapier rod fit in the crowned tooth profile of the tooth of the cooperating drive pinion, which in this way leads to a redistribution of Hertzian pressure, eliminating or reducing peak loads at the teeth ends without overloading the tooth aperture in the middle of the tooth width.

In this way the Hertzian stresses that occur at the contact spot between teeth apertures of the rapier rod and at least one tooth of the cooperating drive pinion are redistributed over the width of the tooth and the tooth aperture in such a way that stresses at the end of the tooth (in widthwise-direction) reduce and the distribution of stress over the contact spot between rapier rod and drive pinion becomes more evenly. In consequence occurring peak loads reduce on the one hand and peak load is shifted from the end of the tooth width (fringe areas) to the middle of the tooth width on the other hand. As a consequence peak load is situated at a less vulnerable spot, further away from the rounding in the tooth apertures of the rapier rod, which are the risk areas for formation of notch effect.

In a preferential embodiment of the drive pinion according to the invention, the named tooth (3) is shaped involute. Consequently a drive pinion with involute profiled teeth is obtained.

In a preferred embodiment of the drive pinion according to the invention, the shape of at least one of the tooth flanks of a tooth is shaped as a circular arc.

In yet another embodiment of the drive pinion according to the invention, the form of at least one of the tooth flanks is shaped according to a logarithmic curve. A tooth form shaped according to a logarithmic curve differs from a tooth form shaped according to a circular arc in that the tooth form according to a logarithmic curve has a smaller tooth thickness difference in the middle area, whereas the tooth thickness difference in the fringe areas according to the logarithmic curve is larger than for a tooth form according to a circular arc. This has as an advantage that in case of a tooth form according to a logarithmic curve the increase of the air gap between the tooth of the drive pinion and the tooth aperture in the free of load rapier rod starting from the middle of the tooth up to the edge firstly increases slower than in case of the embodiment according to a circular arc and toward the edge of the tooth width increases much faster than in case of an embodiment according to a circular arc.

This preferred embodiment allows reducing acting stresses on the outer side without having to considerably increase stress in the middle of the set of teeth.

In a most particular embodiment of the drive pinion according to the invention, the difference between tooth thickness in the middle area and tooth thickness in the fringe areas is situated between 1 and 20% of the tooth width.

In a particularly advantageous embodiment of the drive pinion according to the invention, the tooth shape of at least one tooth of the drive pinion symmetrically covers both sides of the middle area.

Another subject of this patent application relates to a rapier device for a weaving machine, comprising a rapier rod actuated by a drive pinion, whereby it concerns a drive pinion according to one of the claims 1 up to and including 7.

Furthermore, this patent application relates to a rapier-weaving machine, which is equipped with one or more rapier devices according to claim 8.

In order to further explain the features of this invention and to indicate additional advantages and details, the equipment according to the invention will now be described more into detail. Let it be clear that nothing in the following description may be interpreted as a limitation of the protection as required in the claims for this invention.

In this description reference is made to the accompanying drawings using reference numbers, and wherein:

FIG. 1 shows a cross-section of the meshing of a number of teeth of the drive pinion with the tooth profile of the cooperating rapier rod, according to the state of technique, without crowning with indication of the spread of Hertzian pressure;

FIG. 2 shows a cross-section of the meshing of a number of teeth of the drive pinion with the tooth profile of the cooperating rapier rod, with application of crowning of the tooth according to the invention, with indication of the spread of Hertzian pressure;

FIG. 3 shows a front view of the drive pinion according to the invention;

FIG. 4 shows a cross-section B-B of one tooth from the drive pinion according to FIG. 3;

FIG. 5 shows a perspective view of one tooth of a drive pinion according to the invention.

This invention relates amongst others to a drive pinion (1) for actuating a rapier rod (2) of a weaving machine, comprising a set of teeth (3) disposed to mesh with a tooth profile (4) of a cooperating rapier rod (2), whereby the tooth thickness (Td) of at least one tooth (3) of the drive pinion (1) varies according to the widthwise-direction (Tb) of the tooth, and in which this tooth thickness (Td) is larger in the middle area (5) than it is at the fringe areas (7), in order to achieve in this way a redistribution of Hertzian pressure, reducing or eliminating the peak load in the fringe areas of the tooth (3). The widthwise-direction is the direction transversely to the outline (centre line (6)) of the pinion (1).

Fact is that for drive pinions according to the state of technique with involute profiled teeth, acting Hertzian forces (see FIG. 1), that occur at the contact between the aperture provided in the rapier rod and the tooth of the cooperating drive pinion, increase toward the edges of the involute profiled teeth. At the edges of these teeth, stresses may be up to more than 40% higher than in the middle of the tooth.

In crowning the teeth (3) of the cooperating drive pinion (1) represented in FIG. 1 in widthwise-direction of the tooth (3), this means that tooth thickness reduces progressively from the outline or centre line (6) of the pinion (1), Hertzian stress will be redistributed, as represented in FIG. 2, over the width of the tooth (3) in such a way that stresses at the ends of the tooth, in fringe areas (7) reduce and through which distribution of stress over the engagement plane becomes more evenly. Consequently occurring peak loads reduce on the one hand, and peak load is shifted from the end of the tooth width to the middle of the tooth width on the other hand. As represented in FIG. 2, peak load is now situated in a less vulnerable area, further away of the roundings in the rapier rod, considerably reducing the risk of notch effect.

The difference between tooth thickness in de middle area (Tdm) and tooth thickness in the fringe areas (Tdr) is situated between 1 and 20% of the tooth width (Tb). In this way, thickness of a tooth with a maximum tooth width of 8 mm may vary to over 1.6 mm.

As represented in FIG. 4, tooth thickness may reduce either according to a circular arc, through which the tooth shape in tooth width develops according to a circular arc with radius R.

Or tooth thickness decreases logarithmically. 

1. Drive pinion (1) for actuating a rapier rod (2) of a weaving machine, comprising a set of teeth (3) which are disposed in such a way that they engage a tooth profile (4) of a cooperating rapier rod (2), characterized in that the tooth thickness (Td) of at least one tooth (3) of the drive pinion (1) varies according to the widthwise-direction (Tb) of the tooth, and in that this tooth thickness (Td) is larger in the middle area (5) than it is in the fringe areas (7).
 2. Drive pinion (1) according to claim 1, characterized in that said tooth (3) is shaped as an involute.
 3. Drive pinion (1) according to claim 1, characterized in that tooth thickness progressively reduces from the middle area (5) on.
 4. Drive pinion (1) according to claim 1, characterized in that the shape of at least one of the tooth flanks (8) of a tooth (3) is shaped as a circular arc.
 5. Drive pinion (1) according to claim 1, characterized in that the shape of at least one of the tooth flanks (8) of a tooth (3) is shaped according to a logarithmic curve.
 6. Drive pinion (1) according to claim 1, characterized in that the difference between tooth thickness in the middle area (Tdm) and tooth thickness in the fringe areas (Tdr) is situated between 1 and 20% of tooth width (Tb).
 7. Drive pinion (1) according to claim 1, characterized in that the tooth shape of at least one tooth (3) of the drive pinion (1) symmetrically covers both sides of the middle area (5).
 8. Rapier device for a weaving machine, including a rapier rod (2) actuated by a drive pinion (1), characterized in that it concerns a drive pinion (1) in the embodiment of claim
 1. 9. Rapier weaving machine, characterized in that the said rapier weaving machine is equipped with one or more rapier devices according to claim
 8. 